Наблюдатель (Observer)

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Linq;

class Program
{
   static void Main(string[] args)
   {
    Stock stock = new Stock();
    Bank bank = new Bank("Юнит Банк", stock);
    Brocker brocker = new Brocker("Иваныч", stock);

    stock.Market();

    brocker.StopTrade();

    stock.Market();

    Console.ReadLine();
   }
}

interface IObserver
{
    void Update(Object obj);
}

interface IObservable
{
    void RegisterObserver(IObserver o);
    void RemoveObserver(IObserver o);
    void NotifyObserver();
}

class Stock: IObservable
{
    StockInfo info;

    List<IObserver> observers;

    public Stock()
    {
        observers = new List<IObserver>();
        info = new StockInfo();
    }

    public void RegisterObserver(IObserver o)
    {
        observers.Add(o);
    }

    public void RemoveObserver(IObserver o)
    {
        observers.Remove(o);
    }

    public void NotifyObserver()
    {
        foreach(IObserver n in observers){
            n.Update(info);
        }
    }

    public void Market()
    {
        Random rnd = new Random();
        info.USD = rnd.Next(20, 40);
        info.Euro = rnd.Next(30, 50);
        NotifyObserver();
    }
}

class StockInfo
{
    public int USD{get;set;}
    public int Euro{get;set;}
}

class Brocker: IObserver
{
    public string Name{get;set;}

    IObservable stock;
    public Brocker(string name, IObservable obs)
    {
        this.Name = name;
        this.stock = obs;
        this.stock.RegisterObserver(this);
    }
    public void Update(Object obj)
    {
        StockInfo sInfo = (StockInfo)obj;
        if(sInfo.USD > 30)
            Console.WriteLine("Брокер {0} продает доллары;  Курс доллара: {1}", this.Name, sInfo.USD);
        else
            Console.WriteLine("Брокер {0} покупает доллары;  Курс доллара: {1}", this.Name, sInfo.USD);
    }
    public void StopTrade()
    {
        stock.RegisterObserver(this);
        stock = null;
    }
}

    class Bank: IObserver
    {
        public string Name{get;set;}
        IObservable stock;
        public Bank(string name, IObservable obj)
        {
            this.Name = name;
            stock = obj;
            stock.RegisterObserver(this);
        }
        public void Update(Object obj)
        {
            StockInfo sInfo = (StockInfo)obj;
            if(sInfo.Euro > 40)
                Console.WriteLine("Банк {0} продает евро;  Курс евро: {1}", this.Name, sInfo.Euro);
            else
                Console.WriteLine("Банк {0} покупает евро;  Курс евро: {1}", this.Name, sInfo.Euro);
        }
    }